1899] THE CEREAL RUST PROBLEM 343 



cotton- wool was loosely twisted round the base of each of three plants, 

 extending up the plant about half an inch from the muslin on which 

 the plants were growing. Three circles of stout white sterilised 

 blotting-paper, each with a small hole in the centre and a slit from the 

 hole to the margin, were prepared. One of these blotting-paper collars 

 was placed round the stem of each of the wheat plantlets already 

 enveloped at the base with cotton-wool, on which the blotting-paper 

 rested, and was kept moist by the water conducted by the wool. 

 Fresh uredo-spores of Puccinia glumariim were deposited in abundance, 

 by means of a scalpel, on the damp blotting-paper at a distance of 

 about one line from the stem of one of the plants ; at a distance of 

 about three lines from the stem in the second example, and in a circle 

 about four lines from the stem in the third experiment. 



Within a week of depositing the spores on the blotting-paper, the 

 plant to which the spores were placed nearest drooped and fell over as 

 in the disease known popularly as " damping off." Microscopic 

 examination showed that death was due to a dense weft of mycelium 

 emanating from the germinating uredo-spores that had surrounded the 

 stem of the plant. I could not, however, demonstrate satisfactorily 

 that any of the hyphae had penetrated the tissues of the wheat 

 plant. 



Within eighteen and twenty-two days respectively from the date of 

 placing the spores on the blotting-paper, the two remaining plants 

 showed uredo-pustules on the upper surface of the lowest leaf ; in both 

 instances the pustules appeared at a point about one inch above the 

 blotting-paper. This, however, I do not hold to prove that the 

 mycelium travelled upwards for that distance in the tissues of the leaf, 

 but rather consider that the leaf increased an inch in length between 

 the period of inoculation and the time the pustules first became visible 

 externally. The remaining plants not inoculated remained free from 

 disease. 



The above experiment proves satisfactorily, I think, one point, 

 namely, that it is not necessary that the uredo-spore should be in 

 actual contact with the host-plant to insure inoculation, but that the 

 germ-tube can live for some time as a saprophyte, when, if conditions 

 are favourable, it can enter the tissues of a host-plant and assume 

 parasitic functions. This feature may prove to be of great importance 

 from the practical point of view in combating the disease. During 

 the present season I hope to conduct further experiments for the pur- 

 pose of ascertaining for how long a period the mycelium can grow as a 

 saprophyte without losing its power of inoculating a host-plant, and 

 also what distance it can traverse before effecting the same. 



During the present spring an experiment was conducted on similar 

 lines to the above, only teleutospores were used instead of uredo- 

 spores. In this instance only one out of three infected plants pro- 

 duced uredo pustules, whereas an uninfected or check plant also showed 



